Crane

ABSTRACT

A gantry or portal crane has two longitudinally spaced portals which are connected by longitudinally extending structural members to form therewith a self-supporting structure. The lower ends of the uprights of the portals are provided with wheels which can be swung to a lower position engaging the ground and an upper position removed from the ground in which the lower ends of the portals rest directly on the ground. The upper ends of the portals are provided with traverse members each carrying two transversely spaced hydraulic and cylinder piston units which are connected for universal pivoting movement to them, and which are provided at their free ends with engaging portions for engaging a load. A hydraulic system is provided utilizing four separate hydraulic circuits each connected with one of the cylinder and piston units, a central control by means of which all of the cylinder and piston units can be operated in unison, and individual control valves located on the uprights of the portals by means of which each of these cylinder and piston units can be individually operated.

United States Patent [1 1 Wenzel et al.

[11] 3,759,409 1 Sept. 18,1973

[ 1 CRANE [75] Inventors: Jiirg Wenzel, Freudenberg/Main; Hans Rieschel,Miltenberg/Main, both of Germany [73] Assignee: Joseph HaamannFreudenberger Winden-und Hebezeugfabrik,

Freudenberg/M.-l(irschfurt, Germany [22] Filed: Mar. 4, 1971 [21] Appl.No.: 121,050

[30] Foreign Application Priority Data Mar. 7, 1970 Gennany P 20 10945.9

[52] US. CL. 214/394, 212/11, 280/4323 [51'] Int. Cl B60!) l/64 [58']Field of Search 214/392, 394, 396; 212/4, ll, 14; 280/4323 [56]References Cited UNITED STATES PATENTS 3,513,999 5/1970 Schwartz et al.214/394 2,831,588 4/1958 Seed 214/38 BA 3,080,196 3/1963 Darby 280/4323X 3,362,553 l/1968 Weinmann..... 280/4323 X 3,536,161 10/1970 Clarke214/394 X FOREIGN PATENTS OR APPLICATIONS Germany 212/4 909,994 11/1962Great Britain ..214/392 Primary Examiner-Albert J. MakayAttorney-Michael S. Striker [57] ABSTRACT A gantry or portal crane hastwo longitudinally spaced portals which are connected by longitudinallyextending structural members to form therewith a selfsupportingstructure. The lower ends of the uprights of the portals are providedwith wheels which can be swung to a lower position engaging the groundand an upper position removed from the ground in which the lower ends ofthe portals rest directly on the ground. The upper ends of the portalsare provided with traverse members each carrying two transversely spacedhydraulic and cylinder piston units which are connected for universalpivoting movement to them, and which are provided at their free endswith engaging portions for engaging a load. A hydraulic system isprovided utilizing four separate hydraulic circuits each connected withone of the cylinder and piston units, a central control by means ofwhich all of the cylinder and piston units can be operated in unison,and individual control valves located on the uprights of the portals bymeans of which each of these cylinder and piston units can beindividually operated.

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SHEET 3 0F 4 mmvr on CRANE The present invention relates generally to alifting apparatus, and more particularly to a crane. Still moreparticularly, the present invention relates to a gantry or portal crane.

Cranes of this type are already known. They utilize two longitudinallyspaced portals which are connected by structural members extendingbetween them and uniting them into a self-supporting structure. Theuprights of the portals are provided with wheels or rollers so that whenthe crane engages a load, it can be displaced from one location toanother to which it is intended to deliver the load. This latterfeature, however, poses a problem, because due to the forces acting uponthe crane during such displacement, resulting both from the load thecrane carries and also from stresses originating on uneven surfaces overwhich it must move, these known cranes are exceedingly massive andstrong in their construction and therefore cumbersome. They are, andnecessarily must be, provided with a central hydraulic system which actsboth upon the drive,

the steering mechanism and the load-lifting elements of the crane, andthis is a rather expensive structural feature.

Experience has shown, however, that in many cases it is merely necessaryto lift a load for instance off a vehicle or to deposit a load, or toperform similar operations without having to engage the load with thecrane and to move the crane bodily to another location. The art, havingrecognized this more limited requirement, already provides a type ofcrane in which the wheels secured to the portals will automatically beraised against a biasing force --and the lower ends of the uprights ofthe portals will automatically be lowered into engagement with thegroundas the crane engages a load which acts upon it in downwarddirection. However, it has been found that this construction brings withit a substantial danger of accidents because with a crane so constructedit is possible for the crane to roll and become displaced on an unevensurface before the lower ends of the portal uprights have fully decendedinto engagement with the ground.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide an improved crane of the type under discussionwhich is not possessed of the aforementioned disadvantages.

More particularly, it is an object of the present invention to providesuch an improved crane which is less expensive in its construction thanthose known heretofore.

An additional object of the present invention is to provide such animproved crane which can be operated in a simple manner and whichrequires less and simpler servicing than was known heretofore.

An additional object is to provide such an improved crane which can morereadily be used in different situations and which can be transportedmore easily than those known.

A concomitant object is to provide such an improved crane which can becontrolled by a single operator despite its own size and the size andweight of loads which it is capable of handling.

In pursuance of the above objects, and others which will become apparenthereafter, one feature of the invention resides, briefly stated, in acrane comprising a pair of longitudinally spaced portals each having atleast two uprights provided with upper end portions connected by atraverse, and with lower end portions. Longitudinally extendingstructural members connect the portals to form therewith aself-supporting structure and displacing means at the lower end portionsis provided for displacing the structure along the ground. At least apair of load-engaging elements are pivotably connected to and dependfrom each traverse and these elements each comprise a hydraulic cylinderconnected to the respective traverse, a piston displaceable on thecylinder and having an outwardly projecting piston rod provided with afree end, and an engaging portion on the free end for engaging a load.Furthermore, the novel crane comprises a hydraulic circuit for theelements including a plurality of hydraulic circuits each associatedwith one of the elements, central control means associated with all ofthese circuits for operating all of the elements in unison, andindividual control means each associated with one of these circuits foroperating the elements individually.

A crane constructed in accordance with the present invention overcomesthe disadvantages outlined above with respect to the prior art. It alsoachieves the advantages which have been set forth as desirable, and inparticular it makes possible the handling of largedimensioned and heavyloads under the control of only a single operator. This is highlyadvantageous, not only because it avoids the expense involved in havinga second operator connect and disconnect the load from the crane, butalso in that it avoids the danger to such a second operator which existswhere a crane is centrally controlled by the first operator and wherethe second operator can communicate with the first operator at thecentral control stand only by shouting whereas visual communication mayoften be completely lacking, for instance if the crane engageslarge-dimensioned containers which block the view.

The individual control meansis preferably provided within ready reach ofthe engaging portions on the free end of the respective piston rods, sothat the operator can manipulate the engaging portion of a given pistonrod with one hand, and control the cylinder and piston unit with whichthe piston rod is associated,'with the other hand. Normally, theindividual control means will advantageously be located on the: uprightsof the respective portals. They will usually be in form of controlvalves interposed in the hydraulic circuit associated with therespective cylinder and piston unit.

The cylinder and piston units utilized according to the presentinvention are pivoted for universal movement, for instance by means ofball-joint connections. The use of hydraulically controlled cylinder andpiston units in itself is not novel, but it is known from the prior artonly to use them individually or to mount them at the four corners of aload-lifting structure where they are always engaged at one and the samepoint. The utilization of a universal pivot mount has not heretoforebeen proposed.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic perspectiveview illustrating a crane, according to the present invention, with aload in lifted condition;

FIG. 2 is a side view of a further embodiment;

FIG. 3 shows the embodiment of FIG. 2 in a telescoped condition;

FIG. 4 is an enlarged detailed view of FIG. 2, seen from the left-handside thereof;

FIG. 5 is an enlarged detailed view illustrating the wheel mount of thecrane according to the present invention in a position in which thewheel is ready for displacement of the crane; and

FIG. 6 is a viewsimilar to FIG. 5 but illustrating the wheel mount in aposition in which the crane rests on the lower end portions of theuprights in the portals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail, and firstly the embodiment illustrated in FIG. 1, it will beseen that the crane shown there is a crane construction of light steeltubes which, however, are sufficiently strong for lifting and operatingpurposes. The crane has two portals which are longitudinally spaced andwhich each have two upright posts 1 and a traverse 2 connecting theupper end portions. The portals are connected by longitudinallyextending structural members 3,3 which in turn are connected by diagonalbraces 4. A control platform or gondola S is suspended from one of thestructural members 3 so as to be located closely above the ground andcarries a seat 6 for an operator and a central hydraulic control unit 7including the not separately illustrated hydraulic pump and drivetherefor. By locating the gondola 5 closely above the ground, we obtainthe advantage that the operator can readily move about, that is movefrom the gondola 5 to any other part of the crane, simply by steppingdown onto the ground rather than having to climb down, as is customaryin the known portal cranes where the control platform is located highabove the ground. Furthermore, the operator is afforded a clear view ofthe entire loading area when the load engaged by the crane is in raisedcondition.

According to the invention each of the transverses 2 has connected to itby means of known ball and socket joints two hydraulically operablecylinder andpiston units 8. Thus, these units 8 can be universallypivoted which makes it possible to move the connecting elements 82provided at the free end portions of their piston rods 81 to variousdifferent locations, making it possible to engage the load 10 which isshown in FIG. 1 in broken lines at different locations depending uponindividual requirements. Thus, if for instance the portals are spacedfrom one another longitudinally by a distance of 6 meters, the units 8can engage the load 10 at different locations within the range of 5 and7.5 meters. It goes without saying, of course, that the capability oflateral pivoting movement of the units 8 can be reduced to lesserfigures if this is desired.

The hydraulic system for raising or lowering the load 10 utilizes fourindependent hydraulic circuits each of which is associated with one ofthe units 8. This assures that the units 8 cannot influence one another,for instance, as a result of differential loading. Each of thesecircuits can be controlled from the central control, so that all of theunits 8 can be controlled and operated in unison.

In addition, however, each of the units 8 can be indi' viduallycontrolled, for which purpose there is located within reach of theoperator of the respective piston rod 81 -preferably, and as illustratedin FIG. 1 on the upright 1 adjacent to the respective unit 8 is mountedan individual control valve 78 which is interposed in the associatedcircuit and permits raising or lowering of the piston and piston rod tomake it possible for the operator to engage the engaging portion 82 at adesired location of the load 10. When thus all four engaging portions 82have been individually secured to the load 10 in this manner, furtherraising or lowering movements of the units 8 can be centrally controlledin unison from the central control 7 located on the gondola 5. Becauseof this arrangement, the cylinders 8 will all operate in unison andentirely equally, and the speed of lowering will advantageously bemaintained constant via flow-limiting valves of known construction. Ofcourse, the individual control valves 78 make it possible to operate theunits 8 rapidly for extending or retracting the piston rods when theunits 8 are not connected with a load or when they are connected onlywith a light load.

The crane is movable and for this purpose the lower end portion of eachof the uprights 1 is provided with a wheel 9 which is tumably joumalledin a bifurcated mounting member 91. The mounting members 91 in turn arepivotably connected, as shown by comparison of FIGS. 5 and 6, via an arm92 to member 11 secured to the lower end portion of the respectiveupright l. The member 11 may for instance be welded to the respectiveupright l and the latter are each provided with a base plate 12. In eachof the uprights 1 there is mounted a traversely positioned hydrauliccylinder 71, the piston rod 711 of which abuts against the arm 92 asshown in FIG. 6 so that, when hydraulic fluid is admitted to therespective cylinder 71 via the associated conduit 72, pressure of thepiston rod 711 on the associated arm 92 displaces the respective wheelto groundengaging rolling position, forcing thereby the associatedupright 1 to be lifted off the ground as shown in FIG. 6.

Hydraulic motors 71 with associated gear drives are provided for drivingthe wheels of one of the portals and it is advantageous that theconstruction of these drives is such that the crane can negotiate thecommonly-used ramps having an incline of 14. There are also providedhydraulic brakes (not illustrated) which are so dimensioned that theycan reliably hold the device under operating circumstances.

When the crane is to be moved on its wheels, the hydraulic system isswitched to drive mode in which one of the the four independenthydraulic circuits acts to supply the cylinders 71 and thenon-illustrated steering mechanism. The remaining three circuits can beindividually or jointly switched for supplying the hydraulic motors 73and this makes it possible to obtain three different drives speedswithin which by suitable drive control the speed can be continuouslyvaried.

It will be appreciated that the location of the central control means 7on the gondola 5 has an additional advantage beyond those mentionedearlier, namely that the entire gondola with the control unit, as wellas the pump and the drive therefor, can be constructed as a unit and canbe replaced in case of necessity. Also, this construction facilitatesmaintenance work.

The arrangement and mounting of the wheels in the manner describedcorrects the danger of accidents inherent in the prior-art constructionsbecause accidental rolling displacement of the unit is avoided.Furthermore, overpressure valves in the supply conduits lead ing to thecylinder and piston units controlling the displacement of the wheels,can assure that lifting of the load with the wheels in downwardlydisplaced rolling condition does not lead to damage, for instance of thewheel axles. The weight of the crane itself is relatively small and thismakes it possible to use the simple wheel mounts which have beendisclosed, and also to use solid-rubber wheels rather than the balloonwheels which are customary in the prior art. Of course it is alsopossible to utilize a hydro-pneumatic spring arrangement for even loaddistribution to all four wheels, if desired.

Under certain circumstances, for instance when the crane is to betransported from one location to another, it is desirable to be able tovary its overall dimensions, and more particularly to decrease themtemporarily. For this purpose, the cylinder and piston units whichnormally lift the load, and which as previously pointed out areuniversally mounted by means of ball and socket joints or the like, areconstructed as doubleacting cylinder and piston units capable ofproviding both push and pull action. Hence, sections can be providedwhich can be connected with the free ends of the piston rods of theseunits, and the cylinders of the units can be arrested in uprightposition by being secured to the upper end portions of the respectivelyassociated uprights of the portals. This construction makes itunnecessary to provide separate hydraulic means for moving the portaluprights from the transport position because the piston rods, extendedby the extending sections, can now bear against the ground when theirassociated pistons are operated, thereby causing the uprights which ofcourse in this construction consist of telescopical sectionsto beupwardly extended or telescoped apart. Once they have reached thedesired extended positions, the telescopic sections of the uprights arethen arrested with reference to one another and the cylinders can beretracted and the extending sections removed so that the cylinders willnow be used for engaging a load in the manner discussed earlier.

The affixing and removal of the extending sections is of course greatlysimplified by the provision of the individual control valves whichare'located within reach of the respective cylinder and piston units,and the individual control of each such unit.

The traverses in such a construction may also be made telescopic in thateach is provided with a separate cylinder and piston unit, the cylinderof which is connected with one and the piston or piston rod of which isconnected with the other telescopic section of the respective traverse,so that the traverses may be shortened or lengthened in dependence uponoperation of the respectively associated cylinder and piston unit. Thefilled cylinder chamber, that is the cylinder chamber filled with fluid,here eliminates the need for a separate mechanical arresting arrangementfor arresting the telescopic sections of the traverses in desiredposition. It is advantageous to have the traverses be connected with theupper ends or laterally thereof of the uprights,

so that the interior of the telescopic sections of the tra verses arereadily accessible for maintenance purposes from their open ends.

With such a construction, the portals may be made both narrower andlower, and when the unit has been transported to the location where itis to be used, the portals can then be restored to their original size.The posts of the portals can be telescoped apart while the units arestationary, and the traverses may be telescoped apart while the unitmoves slowly on its wheels. The unit can move on its own wheels, drivenby its own drive, both as its various components are telescoped apartand as they are telescoped together to reduce the size of the unit. Itcan thus move onto and off conventional ramps, including to and from atransporter which may be used for transporting the unit over substantialdistances where moving of the unit under its own drive would not bepracticable.

Such an embodiment is illustrated in FIGS. 2-4. Here, the uprights ofeach portal are each composed of two telescopic sections 1 and 1 and thetraverse of two telescopical sections 2 and 2. The sections arepreferably of quadratic or rectangular cross section. The longitudinallyextending structuralmembers are not telescoped and are again identifiedwith reference numerals 3 and 3', being connected by the diagonal braces4. The control gondola is again identified with reference numeral 5 andhas the seat 6,'being provided with the drive 51 for a hydraulicpump 52and the central control means 7.

A hydraulic cylinder 22 is accommodated in the telescopic sections 2,2of a traverse and has a piston rod 221 which is connected with onesection and a cylinder 222 which is connected with the other section ofthe traverse. The unit 22 can be activatedfrom the gondola 5 as shown inFIG. 4. After its piston rod 221 is extended from the cylinder, fluidflow is blocked and the fluid-filled cylinder chamber makes itunnecessary to provide mechanical arresting means for arresting thesections 2,2 against other telescopic movement. When the sections 2, 2'are to be telescoped together or apart, the crane is advanced on itswheels over a short distance, and during this time the necessarytelescoping action is carried out.

The uprights composed of the sections 1,1 are telescoped by means of thehydraulic cylinder and piston units 8' which replace the units 8 of thepreceding figures. The units 8 are of the double-acting typeand theircylinders can be arrested at the upper end portions of the sections 1 bymeans of arresting means 13. Extending sections83 are releasably securedto the connecting portions 82 on the pistonrods 81 and, when fluid isnow supplied to the cylinders, the piston rods 81 move downwardly untilthe extending sections abut against the ground, thereby raising thetraverse 2,2 with the upper sections 1 with reference to the lowersections 1', that is telescoping the upper sections out of the lowersections 1'. In the selected telescoped position, the sections 1,1 aremechanically connected with one another in suitable manner which doesnot in itself form a part of the present invention, and the device isnow ready for use.

The provision of the separate control valves 78 for near the .uprights1,1' is particularly important, because it makes it possible to connecteach of the individual extending sections 83 with a piston rod, puttingit in place by positioning it on the ground and exerting by suitablycontrolling the extension of the piston rod of the respective cylinderand piston unit 8' light downward pressure to hold it in place until allof the units 8 are similarly provided with the extending sections 83 andcan then be controlled in unison for raising to their desired height.

In FIG. 2 the crane according to the embodiment of FIGS. 2-4, is shownsupported on its uprights and holding the lifted load 10. In FIG. 3 thecrane is shown in telescoped collapsedcondition rolling onto a flatbed101 up a ramp 100 with its wheels 9 and under the action of its owndrive.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in acrane, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. A crane, comprising a pair of longitudinally spaced portals eachhaving at least two uprights provided with upper end portions connectedby a traverse, and with lower end portions; longitudinally extendingstructural members connecting said portals to form therewith aself-supporting structure; displacing means at said lower end portionsfor displacing said structure along the ground; at least a pair ofload-engaging elements pivotably connected to and depending from eachtraverse, said elements each comprising a hydraulic cylinder connectedto the respective traverse, a piston displaceable in said cylinder andhaving an outwardly projecting piston rod provided with a free end, andan engaging portion on said free end for engaging a load; and ahydraulic system for said elements, comprising a plurality of hydrauliccircuits each associated with one of said elements, central controlmeans associated with all of said circuits for operating all of saidelements in unison, and individual control means comprisingindividualvalves each located on one of said uprights and interposed insaid circuits for operating said elements indiv'idually.

2. A crane as defined in claim 1, said hydraulic system furthercomprising a pump, and a drive for said pump; and a control platformsuspended from at least one of said structural members intermediate saidportals and located proximal to the ground, said control platfonnsupporting thereon said pump, drive and central control means of saidhydraulic system.

3. A crane as defined in claim I, said displacing means comprising aplurality of wheel units.

4. A crane as defined inclaim 3, each of said wheel units comprising abifurcated wheel support, pivot means mounting the respective wheelsupport to one of said lower end portions for vertical movement about apivot axis, andat least one wheel mounted in the respective bifurcatedwheel support.

5. A crane as defined in claim 4; and further comprising a plurality ofcylinder and piston units each carried by one of said uprights andcooperating with one of said wheel units in a sense efi'ecting, whenoperated, pivotal displacement of the respective unit in a substantiallyvertical plane from a raised position to a lowered ground-engagingposition.

6. A crane, comprising a pair of longitudinally spaced portals eachhaving at least two uprights provided with upper end portions connectedby a traverse, and with lower end portions; longitudinally extendingstructural members connecting said portals to form therewith aself-supporting structure; displacing means at said lower end portionsfor displacing said structure along the ground; at least a pair ofload-engaging elements pivotably connected to and depending from eachtraverse, said elements each comprising a double-acting hydrauliccylinder connected to the respective traverse, a piston displaceable insaid cylinder and having an outwardly projecting piston rod providedwith a free end, and an enegaging portion on said free end for engaginga load; a hydraulic system for said elements, comprising a plurality ofhydraulic circuits each associated with one of said elements, centralcontrol means associated with all of said circuits for operating all ofsaid elements in unison, and individual control means each associatedwith one of said circuits for operating said elements individually;arresting means for arresting said cylinders in upright orientation; andextension sections connectable with said piston rods for extending thelength thereof so that, at the will of an operator, said elements may beused without said extension sections for engaging a load, or be arrestedin upright orientation and connected with one of said sections.

7. A crane as defined in claim 6, wherein each traverse is composed ofat least two telescopable tubular sections.

8. A crane as defined in claim 7; and further comprising hydrauliccylinder and piston units in each traverse and operable for telescopingsaid tubular sections thereof.

9 A crane as defined in claim 1, said displacing means comprising aplurality of wheel units each having a bifurcated wheel supportpivotably mounted to one of said lower end portions for verticalmovement about a pivot axis, at least one wheel mounted in said wheelsupport, and a hydraulic cylinder and piston unit mounted in therespective upright and having a piston rod acting upon the associatedwheel support for pivot-'- ing the same about said pivot axis. I I k

1. A crane, comprising a pair of longitudinally spaced portals eachhaving at least two uprights provided with upper end portions connectedby a traverse, and with lower end portions; longitudinally extendingstructural members connecting said portals to form therewith aself-supporting structure; displacing means at said lower end portionsfor displacing said structure along the ground; at least a pair ofload-engaging elements pivotably connected to and depending from eachtraverse, said elements each comprising a hydraulic cylinder connectedto the respective traverse, a piston displaceable in said cylinder andhaving an outwardly projecting piston rod provided with a free end, andan engaging portion on said free end for engaging a load; and ahydraulic system for said elements, comprising a plurality of hydrauliccircuits each associated with one of said elements, central controlmeans associated with all of said circuits for operating all of saidelements in unison, and individual control means comprising individualvalves each located on one of said uprights and interposed in saidcircuits for operating said elements individually.
 2. A crane as definedin claim 1, said hydraulic system further comprising a pump, and a drivefor said pump; and a control platform suspended from at least one ofsaid structural members intermediate said portals and located proximalto the ground, said control platform supporting thereon said pump, driveand central control means of said hydraulic system.
 3. A crane asdefined in claim 1, said displacing means comprising a plurality ofwheel units.
 4. A crane as defined in claim 3, each of said wheel unitscomprising a bifurcated wheel support, pivot means mounting therespective wheel support to one of said lower end portions for verticalmovement about a pivot axis, and at least one wheel mounted in therespective bifurcated wheel support.
 5. A crane as defined in claim 4;and further comprising a plurality of cylinder and piston units eachcarried by one of said uprights and cooperating with one of said wheelunits in a sense effecting, when operated, pivotal displacement of therespective unit in a substantially vertical plane from a raised positionto a lowered ground-engaging position.
 6. A crane, comprising a pair oflongitudinally spaced portals each having at least two uprights providedwith upper end portions connected by a traverse, and with lower endportions; longitudinally extending structural members connecting saidportals to form therewith a self-supporting structure; displacing meansat said lower end portions for displacing said structure along theground; at least a pair of load-engaging elements pivotably connected toand depending from each traverse, said elements each comprising adouble-acting hydraulic cylinder connected to the respective traverse, apiston displaceable in said cylinder and having an outwardly projectingpiston rod provided with a free end, and an enegaging portion on saidfree end for engaging a load; a hydraulic system for said elements,comprising a plurality of hydraulic circuits each associated with one ofsaid elements, central control means associated with all of saidcircuits for operating all of said elements in unison, and individualcontrol means each associated with one of said circuits for operatingsaid elements individually; arresting means for arresting said cylindersin upright orientation; and extension sections connectable with saidpiston rods for extending the length thereof so that, at the will of anoperator, said elements may be used without said extension sections forengaging a load, or be arrested in upright orientation and connectedwith one of said sections.
 7. A crane as defined In claim 6, whereineach traverse is composed of at least two telescopable tubular sections.8. A crane as defined in claim 7; and further comprising hydrauliccylinder and piston units in each traverse and operable for telescopingsaid tubular sections thereof. 9 A crane as defined in claim 1, saiddisplacing means comprising a plurality of wheel units each having abifurcated wheel support pivotably mounted to one of said lower endportions for vertical movement about a pivot axis, at least one wheelmounted in said wheel support, and a hydraulic cylinder and piston unitmounted in the respective upright and having a piston rod acting uponthe associated wheel support for pivoting the same about said pivotaxis.